Photographic and other high definition images are conventionally reproduced with a uniform, high gloss surface that enhances the clarity and sharpness of the image. Pigmented inks are desirable for inkjet printers because they can be used on a variety of print media to produce saturated, opaque colors, and are typically more permanent and have greater resistance to ultra-violet light than dye-based inks. However, especially when applied to a print medium with a smooth (glossy) surface, pigmented inks tend to produce an image whose inked portions have a relatively low gloss in comparison with either the surrounding print medium or the corresponding portions of an image printed with dye-based inks. This low gloss is believed to be the result of the ink being deposited on the smooth surface of the glossy paper as loosely packed clumps of discrete pigmented particles held together by a polymeric binder, thereby resulting in a rough (low gloss) surface texture in the inked portions the image. This clumping effect is exacerbated in certain types of aqueous ink systems in which ionic forces normally disperse the individual particles of pigment in a liquid suspension medium, but cause certain combinations of pigmented particles to combine into even larger precipitates.
It is known to apply heat to the liquid ink before and during the printing process to thereby speed up the rate at which the suspension medium can be evaporated or absorbed and the ink thereby becomes sufficiently dry that the printed image will not be subject to smearing when it comes into contact with the printer mechanism or with previously printed media. However, a rapid loss of solvent or other suspension medium encourages the individual particles of pigment to flocculate into distinct clumps rather than remaining dispersed within a more or less homogenous layer.
Conventional print-zone heating not only exacerbates the undesirable clumping of the pigmented particles, but can also cause glossy paper to form undesirable wrinkles at all but the lowest heat settings, particularly when the heat source is a heating element below the print medium.